Figure 5The emission line of aluminium at 8.3 Å (= 1493 eV) split into a doublet by the quartz bent-crystal analyser (Cauchois et al., 1963b, p. 1243). The exposure time was 2.5 min, the detector a photographic film, the blackening of which was then converted into a graph by a microphotometer. The current emission-line energies are 1486.70 and 1486.27 eV.